another random user writes: Just as electronic circuits are made from resistors, capacitors and transistors, biological circuits can be made from genes and regulatory proteins. Engineer Tae Seok Moon’s dream is to design modular “genetic parts” that can be used to build logic controllers inside microbes that will program them to make fuel, clean up pollutants, or kill infectious bacteria or cancerous cells.

The circuit Moon eventually built consisted of four sensors for four different molecules that fed into three two-input AND gates. If all four molecules were present, all three AND gates turned on and the last one produced a reporter protein that fluoresced red, so that the operation of the circuit could be easily monitored.